This invention relates to a liquid crystal colour display device comprising liquid crystal picture elements for displaying three different colours which are arrayed in rows and columns with each column comprising picture elements associated with a respective colour, in which the picture elements are each associated with a respective switching element and are driven via first and second sets of address conductors which cross one another with each row of picture elements being connected with a respective address conductor of the first set and with each address conductor of the second set being connected with a respective picture element in each row and associated with picture elements of more than one colour.
Display devices of this kind are known, for example from EP-A-0244013, and can be used for displaying alpha-numeric or video, e.g. T.V. information. The switching elements may comprise three terminal devices, such as TFTs, or two terminal, non-linear, devices of various forms such as MIMs, back to back diodes, diode rings etc. The picture elements are driven a row at a time by applying scanning signals to each of the first set of address conductors in sequence and synchronised data signals to the address conductors of the other set. The polarity of the drive voltages applied to the picture elements is periodically inverted, in accordance with standard practice, in order to improve display quality.
For visual perception considerations, the lay-out of the colour picture elements is preferably in a so-called delta configuration in which the filter elements are arranged in a triangular pattern. Examples of delta-configuration display devices are described in EP-A-0244013, using TFTs, and in the paper entitled "A 1.7 M Pixel Full-Colour Diode Driven AM-LCD" by M. Vijan et al in SID 90 Digest at pages 530 to 533, using two terminal switching devices. The picture element lay-out is such that each row of picture elements consists of a repeating R (red), G (green) and B (blue) picture element sequence with the picture elements of one row being shifted relative to those of a juxtaposed row by half a period. A display colour triad, or triplet, may then be obtained comprising a triangular group of three picture elements, R, G and B, in which two of the colour picture elements, e.g. R and G are juxtaposed in the same row, and the third element, B, lies in the juxtaposed row of picture elements mid-way below the R and G elements with each row of colour triads therefore being constituted by two rows of picture elements. As described in EP-A-0244013 a column address conductor can be used, and shared, by two adjacent columns of picture elements, comprising, for a column of triads, one of the two picture elements in one row and the third picture element in the juxtaposed row, and each individual column conductor is associated with picture elements of two colours. A similar delta configuration of picture elements may be used also in a display device in which each colour triad is constituted by three adjacent picture elements, one of each colour, in the same row. This has the advantage over the previous arrangement in that a row of colour points can be addressed via a single row conductor rather than two row conductors, but has the disadvantage of reduced horizontal resolution.
In actively-addressed display devices using two or three terminal non-linear devices the capacitance of these active devices can couple part of the data signal applied to a column address conductor onto a picture element when the active device associated with that picture element is in its off-state. If the capacitance of an active device is sufficiently large in relation to the capacitance of the picture element then the amplitude of the signal coupled onto the picture element will produce vertical cross-talk effects whereby the voltage on the picture element, and hence its transmission, is altered by data signal voltages intended for other picture elements associated with the same column conductor. Usually, this effect is greatest if field rate inversion of the column, data, signal is used, but can be reduced in certain kinds of display devices if a line rate inversion drive scheme, intended to eliminate flicker effects, is employed in which the column signal is inverted every line which can result in the effect of capacitive coupling on the rms voltage of the picture element, and hence the effect on its transmission, being reduced. However, the use of this line inversion drive scheme in overcoming problems with cross-talk has limitations. In particular, it is less effective in colour display devices having colour (R,G,B) picture elements arranged in delta configuration of the known kind. Due to the configuration of colour picture elements in relation to respective column conductors significant vertical cross-talk can still occur even if line rate inversion is used.
It is an object of the present invention to provide liquid crystal colour display device in which vertical cross-talk effects are reduced.
It is another object of the present invention to provide a liquid crystal colour display device having a delta configuration of colour picture elements and driven using a line inversion drive scheme which exhibits a reduction in vertical cross-talk effects.